Television receiver



SCpt. 7, 1948. L, w, PARKER 2,448,908

TELEVISION RECEIVER Filed July 15, 1944 Bremse 2759 i f6 27,3 -P- 5 27gINVENTOR W 27e .502055 Zl/ 1001*??? Patented Sept. 7, 1948 UNITED STATESPATENT OFFICE aussos rmvrsloa' asoman A una w. rarer. wwaslae, N. Y. lprima my 1s, 1944, serai No. 544,126 zc calms. (ci. 17a-5.a)

This invention relates to television receivers. and more particularly toa television receiver embodying an improved way of separating andreproducing the video and audio components of the received televisionsignal.

In the conventional television receiver the sound and picture can'iersmust be seperated so that no sound components reach theA video detector,as otherwise the sound modulation will appear on the screen as undesiredpicture interference.

The present standards for the transmission of black-and-white televisionimages, as prescribed by the Federal Communications Commission, requirethat the image be transmitted by a carrier that is amplitude modulatedby the video signals and that the accompanying sound part of the programbe transmitted as a frequency modulation of a sound carrier spaced 4.5megacycles above the video carrier. If the receiver is of thesuperheterodyne type, frequency drift of the local oscillator used tobeat with the sound and image carriers introduces very serious problems,especially in the soundv intermediate frequency channel, and if theradio frequency used is above 100 megacycles, this trouble is verygreatly increased.

In accordance with my invention I am able to produce television picturesof very satisfactory clarity and freedom from interference, particularlyfrom the sound modulation, while at the same time reproducing the soundaccompaniment equally well and eliminating a number of the receivercomponent parts heretofore believed necessary.

In accordance with my invention it is no longer necessary to completelyseparate video and audio components before detection. On the contrary, Ipermit both these components to reach the second detector and utilizethe interaction between them to produce the audio signal. Theconventional sound channel is thus eliminated and a single channel isused for both the video and the audio components of the televisionsignal.

By the application of my invention, I am able to employ an oscillatorwhich may have a frequency inaccuracy of as much as 200 kc. plus orminus without harmful effects on the picture or To produce a-televisionreceiver in which it is not necessary to separate the video and audiocomponents before detection.

To provide such a receiver in which interaction between video and audiocomponents is utilized to produce the audio frequency signal.

' To produce a receiver in which many of the component parts heretoforeconsidered necessary are eliminated, thereby reducing the cost ofconstruction and maintenance of the receiver.

To produce a receiver of the superheterodyne type in which frequencydrift of the oscillator is not a serious problem.

To produce a generally improved and simplined television receiver. l

Stili -other objects and advantages of my invention will be apparentfrom the specification.

The features of novelty which I believe to be characteristic of myinvention are set forth with particuiarity in the appended claims. Myinvention itself, however, both as to its fundamental principles and asto its particular embodiments, will best be understood by reference tothe specification and accompanying drawing, in which Fig. 1 is theacceptance curve of a television receiver to which my invention isapplied,

Fig. 2 is a schematic diagram of a television receiver in accordancewith my invention,

Fig. 3 is a series of curves showing the performance of a televisionreceiver in accordance with my invention,

Fig. 4 is an idealized curve of a receiver in accordance with myinvention, and

Fig. 5 is a detail of one form of circuit which may be employed in thepractice of my invention.

Referring now more particularly to Fig. l, in which the ordinatesrepresent response and the abscissae frequency, the curve X indicatesthe acceptance of a television receiver according to my invention,before using any of the absorption circuits explained with reference toFigs. 3 and 5.

'I'he picture or image carrier is located at the frequency P and thereceiver at this frequency is made to have approximately half itssensitivity. On the lower side band the receiver will accept frequenciesdown to a frequency approximately one and one-half megacycles below thepicture carrier frequency, all frequencies lower than this being rapidlyattenuated.

For frequency increase above the carrier, the sensitivity of thereceiver increases to a substantially constant value, extending overmost of the upper side band, at the upper end of which it begins todecrease', and if the receiver has a broad enough acceptance, both thepicture and the sound carriers (which in the present illustration is 4.5megacycles above the picture carrier) may reach the detector. Inasuperheterodyne receiver it is conventional practice to cause the localheterodyne oscillator to operate at a frequency above the image andsound radio frequency carriers. Under such circumstanceathe sound I. F.carrier S would be of a lower frequency than the image I. F. carrier P.The two I. F. carriers would still be displaced by an amount equal tothe displacement of the two radio frequency carriers.

If the slope of the receiver acceptance curve over the frequencydeviation band of the sound carrier is other than zero, soundfrequencies will pass through the detector and result in interferencevwith the picture in the conventional receiver, and, accordingly, it hasbeen the practice to provide filters ahead of this detector to separatethese two intermediate frequency carriers.

In accordance with my invention, I permit both of these carriers toreach the detector and I utilize the interaction of the two carrierfrequencies to produce a beat frequency of 4.5 megacycles, whichfrequency is passed on to the video amplifier, which may have someamplification at this frequency so that a signal of comparatively largeamplitude, l volt or more, is secured from its output.

The beat frequency thus produced will be the frequency difference ordisplacement between the original image and sound radio frequencycarriers as radiated, and this difference according to presentblack-and-white standards, is 4.5 megacycles. The beat frequency may beproduced by the interaction or heterodyning of the two radio frequencycarriers (in a TRF receiver), or the two I. F. carriers (in asuperheterodyne receiver). In either event, the same beat frequency isproduced.

A circuit employing this principle is diagrammatically indicated in Fig.2, in which I represents the usual doublet antenna, I I asuperheterodyne television receiver having a video output channel IIaand an audio output channel IIb,'

the latter of which may comprise coupling coil I2 tuned by variablecondenser I3 coupled to discriminator input coils I4 and I5 feeding thediscriminator diagrammatically indicated as I6, and the output of whichis supplied to audio frequency amplifier I'I and thence to loud speakerI8.

The final stage of the last video frequency amplifier in the receiver II may be tuned to 4.5 megacycles by a parallel resonant circuit inseries with the plate resistor of the video frequency amplifier tube. Inthis way the video frequency amplifiers work as reflex amplifiersreducing the number of tubes needed in the completed televisionreceiver. Certain precautions must be taken and certain adjustmentsmade, as will be pointed out more in detail.

If the frequency modulated sound carrier falls on a portion of thereceiver selectivity curve which have a slope other than zero, somefrequency discriminator action would take place over the range offrequency swing of the frequency modulated sound carrier, and some audiofrequency signals will be generated which will be present in the videosignal. If the frequency acceptance curve of the receiver be made sobroad as to include the sound carrier. the slope of this curve may bemade approximately zero in the vicinity of the sound carrier: and ifthis is done, no troublesome audio frequency component will begenerated.

However, if the sound carrier is left at the same amplitude as thepicture carrier, the video modulation will appear in the audio frequencysignal and will be dimcult to remove, and also the gain per stage wouldbe reduced because of the greater band width, requiring a greater numberof tubes for the same gain.

In accordance with my invention. I do not make the acceptance curve sowide that the response of the receiver is substantially the same at thesound carrier frequency as over the upper side band of the picturecarrier. I prefer to use a somewhat narrower acceptance so that thesound carrier falls, as indicated in Fig. 1, on the lower portion of theupper side of the selectivity curve, where it is approaching zero, sothat the amplitude of the sound carrier is about 1,50 of the videocarrier. This 1,50 amplitude, however, is not an absolute necessity andmay vary within wide limits above or below this value.

Fig. 3 shows this portion of the curve of Fig. l on an enlarged scale,and it will be observed that over the 150 kc. total frequency swing ofthe sound carrier there is a change in amplitude of curve X. as shown byA, which, in the absence of my invention, would produce audiointerference in the picture. I, therefore, alter curve X to give a curveshown in idealized form in Fig. 4, in which the sound carrier S isreduced to about 1,50 of the intensity of picture carrier P. and theslope of the selectivity curve near the sound carrier is also reduced tosubstantially zero.

Since the idealized curve. as in Figure 4, has zero slope in the regionof carrier S, no frequency discrimination takes place, and consequentlyno demodulated audio frequencies appear in the output of the seconddetector. Also, since the amplitude of the sound carrier is only 5% ofthe amplitude of the picture carrier, a 90% modulation of the picturecarrier will not alter the amplitude of the 4.5 megacycle beat frequencyproduced by the interaction of the sound and picture carriers. This isbecause of the well-known fact that if one of two heterodyningfrequencies is more than twice the amplitude of the other, the beatfre-` quency amplitude cannot be altered by further increasing thelarger one of the two heterodyning frequencies (assuming that a lineardetector, such as a diode, is used to obtain the beat frequency) If themodulation increases above 90 the picture carrier will drop below thenecessary two to one ratio at times, and there may be a downwardmodulation of the 4.5 megacycle carrier, but since the video signal isbroken by blanlcing signals 15,750 times a second, the picture carriercan stay low for only a shorter time than 1/is,15o second. One hundredper cent modulation of the picture carrier may, therefore, cause a15,750 cycle audio tone to reach the audio amplifier, and this may beeither filtered out, or in many instances be disregarded, since aconventional audio frequency amplifier and loud speaker ordinarily willnot reproduce it to any troublesome extent.

No limiter is necessary to remove any video modulation from the audiofrequency. The 60- cycle blanking pulses (with their harmonics withinthe audio frequency range) are of such phase in the system employed inthe United States that they increase the picture carrier and, aspreviously stated, this has no eilect on the 4.5 megacycle beatfrequency. A limiter, however, may be used employed to absorb energyfrom the intermediate frequency coils over a particular range.

In Fig. 5 the tube 20 may be one of the intermediate frequency amplifiertubes preceding the second detector. and this may be a pentodecomprising cathode c, control grid 22cm screen grid 20w, suppressor20sra, and anode 22a. The cathode may be grounded through resistor 221'shunted by by-pass condenser 20h, and the anode 22a may be connectedthrough inductance 2| shunted by tuning condenser 22 and resistance 22to the source of B voltage.

Coupled to the inductance 2| I may provide additional inductance 24shunted by tuning condenser 25 and by resistance 26. one common point ofsaid elements being connected to ground and the other to the controlgrid Non of tube 27. which may also be a pentode, having cathode 21e,control grid Tico. screen grid 21.10, suppressor 21srg, and anode 21a.The cathode of this tube may be connected to ground through resistance28 shunted by by-pass condenser 28.

Coupled to the inductances 2| and 24 I may provide an additionalinductance 2li shunted by resistance 2|, and by tuning condenser 22, andthis may constitute an absorption circuit or wave trap. This absorptioncircuit is preferably tuned to a frequency spaced 150 kc. l(or any othersuitable amount) from the sound carrier in the direction of the videocarrier. By control of the parameters of this absorption circuit; thatis. by varying the tuning, the damping, and the coupling of thiscircuit. it is possible to obtain a curve Y which is substantially themirror image of the curve X over the range of frequency swing of thesound carrier.

The overall acceptance of the receiver with the absorption circuit orwave trap so adjusted is. therefore, the resultant of the two curves Xand Y. and is shown by the dot and dash curve. X-l-Y. from which it willbe seen that the total change in slope of the acceptance over the 150kc. swing of the sound carrier, as indicated by B, is a very smallproportion of the change which would otherwise be obtained. as indicatedat A.

It is possible to reduce the audio frequency interference from thepicture without using the absorption circuits shown with reference toFigs. 3 and 5 by reducing the audio frequency carrier amplitude to avalue much lower than l/io of the picture carrier amplitude: forexample, x/wa This, while it simplifies construction, is not alwaysdesirable. since the audio frequency signal becomes very low and makesadditional amplification necessary.

While I have described my invention particularly with reference to itsincorporation in a receiver of the superheterodyne type. it is to beunderstood that my invention is not limited thereto and may be employedwith tuned radio frequency receivers. In present television receivers ofthe superheterodyne type the local oscillator must be adjusted withinthe limits of plus or minus 10 kc., for instance. in order to keep thesound carrier at the proper point on the discriminator curve: but withthe employment of my invention this is no longer necessary, and anoscillator change of plus or minus 200 kc. may occur without harmfuleil'ects on picture or sound.

In applying my invention to a TRF receiver, the radio frequencyamplifier is treated in the same way as the intermediate frequencyamplifier in the superheterodyne receiver already described; that is.absorption circuits or wave traps, asshown in Fig. 5, are introducedapproximately 6 iokabeiowthesoimdcarrierfrequenc! (i. e..inthedireetionofthevideocarrier')andthsparamstersofthecircuitaresocontrolledasto obtain an absorptioncurve which is lsubstantially the mirror image of the selectivity curveof the sound carrier frequency swing.

Inthesuperhetcrodynereceiveritwillgeneraily not be necessary to alterthe selectivity of the preselector since this usually will4 notintroduce enoughl audio frequency components into the picture to make itworth while to use absorption circuits. However. this may be done ifdesired.

It may be noted that in applying this invention to a luperheterodyne orTRP receiver the 4.5 megacycle frequency modulated best frequencycarrier that is extracted from the output oi' the video amplifier by thediscriminator I2, which may be tuned to 4.5 mc. has such high amplitudethatordinarliyonlytwoorthreetubesarenecessary to receive the soundaccompaniment instead of the usual five tubes.

While I have shown and described certain preferrrd embodiments of myinvention, it will be understood that modifications and changes may bemade without departing from the spirit and scope thereofI as will beclear to those skilled in the art.

In this application I have particularly pointed out and distinctlyclaimed the part, improvement, or combination which I claim as myinvention or discovery. and I have explained the principles thereof andthe best mode in which I have contemplated applying those principles soas to distinguish my invention from other inventions.

I claim:

l. In a television receiver for a television system in which a picturesignal carrier is amplitude modulated and the complemental sound signalis transmitted as a frequency modulation of a second carrier, incombination, an amplifier, means for supplying said picture and soundcarriers of a television signal to said amplifier, a detector suppliedby said amplifier, and a selecting circuit connected between saidamplifier and `said detector and having a frequency characteristic suchthat both picture and sound carriers are passed to said detector, thetwo carriers being heterodyned with each other in the detector, andmeans in the selecting circuit for modifying the characteristics of thatcircuit so that it is characterized by substantially zero slope over therange of frequency swing of the sound carrier and has an amplitude levelbelow the minimum modulated amplitude of the amplitude-modulated picturesignal carrier, whereby the output from said detector contains bothdetected video signals and undetected frequency modulated audio signals,and a detectorresponsive to the undetected signals to produce the audiosignals.

2. In a television receiver, adapted to receive upon an antennaconcomitantly transmitted video and audio signals supplied upon twocarriers having substantially constant frequency separation and in whichone carrier is frequency modulated by one of the signals and the othercarrier is amplitude modulated by the other signal, in combination, aselecting circuit supplied with said received signals, said selectingcircuit having a frequency characteristic such that both picture andsound carriers of the same television signal4 as accepted thereby aresupplied therefrom in an amplitude ratio which is of the order of 20:1.means for heterodyning said accepted carriers with each other to producea third car. rier. and a detector for said third can'ier.

3. The method of receiving a television frequency band including videoand sound signals on carriers 4.5 megacycles apart, with the videocarrier amplitude modulated and the sound carrier frequency modulatedwhich comprises the steps of selectivity amplifying the two carriers toproduce video and audio components in a substantially 20:1 amplituderatio in a common channel, and heterodynlng saidvideo and audiocomponents with each other to provide a frequency modulated oscillationof 4.5 megacycles carrying the sound signal and substantially free fromvideo modulation.

4. In a television receiver for receiving television -signals consistingof an amplitude modulated video signal carrier and a related frequencymodulated audio signal carrier,l the two carriers being separated by asubstantially fixed frequency difference. in combination, means forreceiving incoming signals, including a selecting circuit having anoverall selectivity curve providing substantial cut-off 1.5 megacycleson one side of the video frequency, increasing to substantially halfamplitude at video carrier frequency and full amplitude oversubstantially the entire video sideband on the other side of the videocarrier, and decreasing to the order of las maximum amplitude in theregion of the audio carrier frequency, means operating conjointly withsaid selecting circuit and having a selectivity curve which issubstantially the mirror image of the selectivity curve of saidselecting circuit in the region of the audio carrier, said means beingeffective to establish a resultant selectivity curve in the region ofthe audio carrier for substantially preventing amplitude modulation ofthe audio carrier, detecting means energized from the selecting circuitfor beating together and amplitude detecting the modulated carriers fromsaid selecting circuit, and means energized from said detecting meansfor reproducing audio frequency signals from the resulting frequencymodulated beat frequency.

5. In a television receiver for receiving television signals consistingof an amplitude modulated video carrier and a related frequencymodulated audio carrier. the two carriers being separated by asubstantially fixed frequency difference, in combination, means forreceiving incoming signals, including a selecting circuit having anoverall selectivity curve providing substantial cut-off 1.5 megacycleson one side of the video frequency carrier, increasing to half amplitudeat video carrier frequency and full amplitude over substantially theentire video sfdeband on the other side of the video carrier frequency,and decreasing to substantially l/zii maximum amplitude in the region ofthe audio carrier frequency, means having a selectivity curve which issubstantially the mirror image of said selecting circuit in the regionof the audio carrier for substantially preventing amplitude modulationof the audio carrier, said last mentioned means modifying the action ofsaid selecting circuit to provide substantially zero frequencyselectivity over the swing of the audio frequency carrier, meansincluding detecting means, and energized from the selecting circuit forbeating together and for amplitude detecting the modulated carriers fromsaid selecting detecting circuit, and a circuit connected to receive theproduced beat frequency output.

6. In a television receiver for receiving television signals consistingof an amplitude modulated video signal carrier and a related frequencyduced as a result of audio carrier frequency deviations, and anabsorption circuit coupled to said selector circuits, said absorptioncircuit being tuned to a frequency spaced substantially 150 kc. from theaudio carrier in the direction of the video carrier, whereby thefrequency characteristics of the selector circuits is modified toestablish a resultant or net frequency characteristic that issubstantially flat or constant, so that amplitude variations in theaudio frequency carrier are substantially prevented, and means energizedfrom the selector circuits for he'terodyning the two carriers to producea beat frequency carrier, and means for detecting the beat frequencycarrier.

7. The method of receiving a television signal frequency band includingrelated video and sound signals on separated carriers, the video carrierbeing amplitude modulated and the sound carrier being frequencymodulated with the carriers separated by a substantially constantfrequency difference, which comprises the steps of amplifying the twocarriers in a common channel to different average amplitudes such thatwhen the video carrier is to be modulated m percent, the sound carriermay have a maximum amplitude not in excess of (1GO-m) percent of theaverage amplitude of the video carrier, heterodyning the video and thesound carriers with each other to produce a beat note having a frequencyequal to the difference between the original separation of the video andthe sound signal carriers, simultaneously detecting the amplitudemodulated video carrier to derive a video component, and amplifying thevideo component together with said beat note, and then separating outthe beat note to derive the sound signal therefrom, and passing thevideo component to a video signal reproduction system and the soundsignal to an audio signal reproducer.

8. The method of receiving a television signal frequency band includingrelated video and audio signals on separate carriers, the video carrierbeing amplitude modulated and the audio carrier being frequencymodulated with the carriers separated by a predetermined substantiallyfixed frequency difference, which comprises the steps of amplifying thetwo carriers in a common channel to different average amplitudes suchthat when the video carrier' is to be modulated m percent, the soundcarrier may have a maximum amplitude not in excess of (10G-m) percent ofthe modulated audio signal carrier. the two carriers being separated bya substantially fixed frequency difference, in combination, anamplifier, a detector supplied with both audio and video carriers bysaid ampiiner, and a selector circuit preceding said detector andincluding means to cause the frequency characteristic of the selectingcircuit to be such that the amplitude of the audio carrier supplied tosaid detector is substantially constant with frequency change and not inexcess of the minimum value of the video carrier at the maximummodulation of said video carrier, whereby said detector output containsboth detected. amplitude modulated video signals and undetectedfrequency modulated audio signals.

10. In a television receiver for receiving a television signal bandconsisting of an amplitude modulated video signal carrier and a relatedfrequency modulated audio signal carrier, the two carriers beingseparated by a substantially fixed frequency difference, in combination,a selecting circuit adapted to be supplied with said signal carriers,said selecting circuit including means to cause the circuitcharacteristic to be such that the picture and the sound carriers of thesame television signal band, as accepted, are amplified in an amplituderatio of the order of 20:1, with substantially zero amplitude change ofthe audio carrier with frequency change, means for heterodyning anddetecting said carriers to produce both a detected video signal and anundetected frequency modulated audio carrier.

l1. The method of receiving a television signal band including video andsound signals on carriers separated by a substantially fixed frequencyseparation of the order of 4.5 megacycles. with the video carrieramplitude modulated and the sound carrier frequency modulated, saidmethod comprising the steps of conducting the carriers of a receivedsignal band through a common channel and amplifying the carriers, asreceived, so that the maximum amplitude of the sound carrier will beless than the minimum value of the video carrier 'at the maximummodulation of said video carrier, .heterodyning the video and the soundcarriers of the received signal band with each other to produce a beatnote of the order of the original frequency separation of 4.5megacycles, simultaneously detecting the amplitude modulated videocarrier to derive a video signal component, amplifying the videocomponent together with the beat note, and then separating out said beatnote and detecting the sound signal therefrom.

12. In a television system, in which the picture signal is radiated onan amplitude modulated carrier and the sound signal on a frequencymodulated carrier separated from the picture carrier by a substantiallyconstant frequency dierence within an allotted transmission band, themethod of receiving and reproducing the picture and the sound signals inproper relationship, which comprises the steps Aof receiving the tworadiated carriers of the transmission band, heterodyning the carriers ofthe transmission band with a locally generated frequency to convert theincoming earriers to I. F. carriers, transmitting the I. F. car riersthrough a common channel with the amplication of the picture signal I.F. carrier relative to the sound signal I. F. carrier made such that anyminimum value of the picture carrier due to its amplitude modulationshall be greater than any maximum value of the sound carrier,heterodyning and amplitude detecting the picture and 10 the sound I. F,carriers to produce the picture video band and a beat frequency carrierof the order of the original frequency difference between the radiatedcarrier frequencies, amplifying the detected picture video band and thesaid beat frequency carrier, feeding the picture video band to the videooutput picture reproducing device while simultaneously separating thefrequency modulatedenergy of the beat frequency carrier from the picturevideo band, detecting said separated carrier to obtain a sound signalcorresponding to the sound intelligence as radiated, and feeding thesound signal to a sound reproducing device.

13. The method of operating a receiver of the superheterodyne type forreceiving a television signal comprising an amplitude modulated videosignal carrier of one frequency and a related frequency modulated audiosignal carrier of a second frequency separated from the video carrier bya substantially constant frequency spacing, which comprises the steps offeeding the two carriers to a first detector or converter for conversionto intermediate frequency carriers having a like frequency spacing,selectively amplifying the two I. F. carriers in a common I. F. channelso that the maximum amplitude of the audio signal carrier is less thanthe minimum value of the video signal carrier, deriving from the I. F.signal channel a beat frequency carrier having a frequency correspondingto the original frequency spacing between the video signal carrier andthe audio signal carrier, and also deriving from the I. F, signalchannel a detected video signal, feeding the detected video signal to animage reproducing tube, feeding the derived beat frequency carrier to afrequency discriminator to develop the audio signal therefrom, andenergizing a sound reproducer with the sound audio signal.

14. The method of operating a superheterodyne television receiver todetect the related sound and video signals of a television broadcast, inwhich the video carrier is amplitude modulated and the sound carrier isfrequency modulated, the two carriers being separated by a predeterminedsubstantially constant frequency difference, which comprises the stepsof receiving and converting the two carriers to two corresponding I. F.carriers separated by a similar frequency difference, transmitting bothI. F. carriers with their modulating intelligence through a common I, F.amplifying circuit and amplifying the sound carrier to a. level ofamplification that is less than the minimum value of the video carrierat maximum modulation of said video carrier, demodulating the amplifiedamplitude modulated video L F. carrier to derive the video signal,heterodyning both I. F. carriers to provide a resultant output beatfrequency carrier that is frequency modulated according to the soundsignal intelligence, and thereafter deriving the sound signal from thebeat frequency carrier for delivery to a sound reproducing device whilethe derived video signal is fed to a picture reproducing device.

15. A television receiver for receiving a selected television signalband which includes two separate radio frequency carriers for conveyingthe video and audio intelligence, one of the carriers being amplitudemodulated by the intelligence conveyed thereby and the other carrierbeing frequency modulated by the intelligence conveyed thereby, the twocarriers being displaced from each other by a predetermined relativelyilxed frequency spacing, said receiver comprising amplifying means toselectively amplify the two carrier frequencies so that the maximumamplitude l 1 of the frequency-modulated carrier is less than theminimum amplitude, of the amplitude-modulated carrier. means forheterodyning the amplified carriers to produce a beat'frcquency carrierof a frequency equal to the frequency spacing between the video carrierand the audio carrier, the beat frequency carrier being frequencymodulated in accordance with the frequency modulation present on theoriginally received frequency modulated carrier. means energized by thebeat frequency carrier and including a frequency discriminator fordemodulating the beat frequency carrier to produce one intelligence,'andmeans including an amplitude detector energized by and operative todemodulate the amplified amplitude modulated carrier to produce anotherintelligence.

16. A television 'receiver for receiving a television signal bandincluding an amplitude modulated image carrier and a related frequencymodulated sound carrier spaced a substantially fixed frequency from thepicture carrier, said receiver comprising means to select and amplifyone such band of frequencies so thatthe amplitude of the sound carrierwill be less than the amplitude of the image carrier at the maximummodulation of that carrier by the picture or image signal. means forheterodyning said carriers to produce a new carrier having a frequencyequal to the frequency spacing of the image and sound carriers and foramplitude detecting the image carrier to produce image-signals, anddemodulating means energized in accordance with the new carrier forproducing audio signals.

17. A television receiver comprising an incoming selecting circuit forsimultaneously receiving two spaced carriers having different types ofmodulation, one carrier being amplitude-modulated and the other carrierfrequency-modulated said receiver including frequency converting meansto convert the received carriers to two local similarly spaced I. F.carriers, means constituting a common I. F. amplifying channel connectedto be energized from the frequency converting means and having asuflicient band width to transmit both I. F. carriers but having suchfrequency characteristic as to transmit the frequency-modulated carrierat an amplitude of the order of 5% of the amplitude-modulated carrier.heterodyning and detector means connected to be energized from the I. F.channel in order to detect one of the I. F. carriers and to heterodynethe two l F. carriers to produce a beat frequency carrier, a subsequentdetector connected to be energized by the output of the heterodyningmeans for detecting the produced beat frequency carrier, and reproducingmeans energized by the two detected outputs.

18. A television receiver for receiving a television signal bandincluding a picture carrier and a sound carrier spaced a substantiallyfixed fre` quency difference apart within the signal band the picturecarrier being amplitude-modulated and the sound carrier beingfrequency-modulated. said receiver comprising means to select andamplify one such television signa1 band, said means including frequencyconverting means to convert the two carriers of said band to twocorresponding I. F. carriers, means constituting a common transmissionchannel to amplify the two I. F. carriers, means constituting part ofthe transmissionchannel for controlling the unequal amplification of thetwo carriers according to a predetermined ratio such that when thepicture carrier is to be modulated m percent, so that its minimummodulated value will be (D-m) percent of the average amplitude of thepicture carrier, then the sound carrier may be given an arnplitude whosemaximum shall not be in excess of said (1D0-m) percent, means energizedfrom the transmission channel to heterodyne and to detect the two I. F.carriers to produce the demodulated intelligence of the greater of thetwo I. F. carriers and to also produce a beat frequency carrier having afrequency equal to the frequency difference between the two carriers,and an additional detector tuned to said beat frequency for extractingtherefrom the intelligence of the lesser I. F. carrier.

-19. A television receiver tfor receiving and reproducing intelligencefrom a distance, which is modulated onto and transmitted by an amplitudemodulated video signa1 carrier and a frequency modulated audio signalcarrier spaced a predetermined relatively fixed frequency distance apartwithin an allotted television signal frequency band, said receivercomprising an incoming selecting circuit including frequency Aconvertingmeans to select a desired television band and to convert the incomingcarriers to two corresponding video and audio I. F. carriers similarlyspaced and carrying the intelligence modulated onto the correspondingincoming carriers, an I. F. amplifying circuit of sufficient band widthto accommodate the two spaced video and audio I. F. carrlers, means toapply both the I. F. carriers to the common I. F. amplifying circuit foramplification thereby so the audio carrier will be of the order of 5% ofthe video carrier, means including a detect-or and energized from the I.F. amplifying circuit to detect the video I. F. carrier to obtaintherefrom the modulated intelligence carried thereon. and to heterodynethe video and audio I. F. carriers to produce a beat frequency carrierof a frequency equal to the frequency spacing between the two I. F.carriers, the beat frequency carrier including the intelligence carriedby the audio I. F. carrier, means including a subsequent detectorenergized by the beat frequency carrier to detect the beat frequencycarrier to obtain therefrom themodulated intelligence transferredthereto from the audio I. F. carrier, and means energized by theintelligence obtained from both detectors for reproducing the originaltelevision intelligence as modulated onto the original carriers of thetelevision signal band.

20. In -a television receiver for receiving a television signa1 bandconsisting of an amplitude modulated video signal carrier and a relatedfrequency modulated audio signal carrier, the two carriers beingseparated by a substantially fixed frequency difference, the combinationcomprising a selecting circuit adapted to be supplied with said signalcarriers, means energized from the selecting circuit for detecting thevideo carrier to derive the video signal therefrom, means forsubstantially preventing sound interference with the video signal, meansenergized from the selecting circuit to use the video carrier as asource of fixed oscillator frequency and to beat it with the audiosignal carrier to establish a new beat frequency carrier for the audiosignal, said beat frequency carrier having a frequency equal to thefrequency difference between the original video and audio carriersl andmeans for frequency detecting the beat frequency carrier to obtain theaudio signal therefrom.

21. In a television receiver for receiving a television signal bandconsisting of an amplitude modulated video signal carrier and a relatedfrequency modulatedaudio signal carrier, the two 13 carriers beingseparated by a substantially fixed frequency difference, the combinationcomprising a selecting circuit adapted to be supplied with said signalcarrie means energized from the selecting circuit icy' detecting thevideo carrier to derive the video vsignal therefrom, means forsubstantially preventing sound interference with the video signal. meansenergized from the selecting circuit to use the-video carrier as asource of fixed oscillator frequency and to beat it with the audiosignal carrier to establish a new beat frequency carrier for thefrequency-modulated audio signal, said beat frequency carrier having afrequency equal to the frequency difference between the original videoand audio carriers, an output circuit to receive the beat frequencycarrier and including elements forming a parallel resonant circuit tunedto said beat frequency, and a frequency discriminator energized fromsaid tuned circuit to frequency detect the beat frequency to derive thefrequency-modulated audio signal therefrom.

22. A television receiver for receiving and reproducing a televisionsignal band including an amplitude modulated video carrier of fixedfrequency and a frequency modulated audio carrier spaced a constantfrequency difference from the video carrier; said receiver comprising aselecting circuit with means for converting the carriers of a selectedtelevision signal band to I. F. carriers spaced an equal constantfrequency distance apart; an I. F. amplifier circuit for the I. F.carriers; amplitude detecting means energized from the I. F. amplifiercircuit for detecting the video signal from the video I. F. carrier;means for substantially preventing sound-interference with thevideo'signal a frequency discriminator for detecting the frequencymodulated audio signal, said discriminator being tuned to a frequencycorresponding to the frequency difference between the video carrier andthe audio carrier;

and means connected to the I F. circuit to re-l ceive and beat the videoand the audio I. F. carriers to derive a beat frequency carriertherefrom and to supply the beat carrier to the discriminator with apredetermined limited amplitude.

23. A television receiver for receiving and reproducing intelligencefrom a distance, which is modulated onto and transmitted by an amplitudemodulated video signal carrier and a frequency modulated audio signalcarrier spaced a predetermined relatively fixed frequency distance apartwithin an allotted television signal frequency band, said receivercomprising an incoming selecting circuit including frequency convertingmeans to select a desired television band and to convert the incomingcarriers to two corresponding video and audio I. F. carriers similarlyspaced and carrying the intelligence modulated onto the correspondingincoming carriers, an I. F. amplifying circuit of sufficient band widthto accommodate the two spaced video and audio I. F. carriers, means toapply both the I. F. carriers to the common I. F, amplifying circuit foramplification thereby, means energized from the I. F. circuit to detectthe video I. F. carrier to derive the video signal therefrom. means forsubstantially preventing sound interference with the video signal meansenergized from the I. F. circuit and using the video I. F. carrier as asource of fixed oscillator frequency to beat with the frequencymodulated I. F. audio signal carrier to establish a new beatfrequencycarrier for the audio signal band with said new beat frequency carrierhaving a frequency equal to the frequency difference between theoriginal video and audio carriers, an

output circuit for receiving said beat frequency carrier and includingelements forming a parallel resonant circuit tuned to said beatfrequency, and a frequency discriminator energized from said tunedcircuit to detect the beat frequency carrier to obtain the audio signaltherefrom.

24. A television receiver for receiving and reproducing intelligencefrom a distance, which is modulated onto and transmitted by an amplitudemodulated video signal carrier anda frequency modulated audio signalcarrier spaced a predetermined relatively fixed frequency-distance apartwithin an allotted television signal frequency band, said receivercomprising an incoming selecting circuit including frequency convertingmeans to select a desired television band and to convert the incomingcarriers to two correspond ing video and audio I. F. carriers similarlyspaced and carrying the intelligence modulated onto the correspondingincoming carriers, an I. F. amplifying circuit of sumcient band width toaccommodate the two spaced video and audio I. F. carriers, means toapply both the I. F. carriers to the common I. F. amplifying circuit foramplification thereby, means energized from the I. F. circuit to detectthe video I. F. carrier to derive the video signal therefrom, means forsubstantially preventing sound interference with the video signal meansenergized from the I. F. circuit and using the video I. F. carrier as asource of fixed oscillator frequency to beat with the frequencymodulated I. F. audio signal carrier to establish a new beat frequencycarrier for the audio signal and having a frequency equal to thefrequency difference between the original video and audio carriers, anoutput circuit for receiving said beat frequency carrier and tuned tosaid beat frequency. a frequency discriminator energized from saidoutput circuit to detect the beat frequency carrier, and means forlimiting the amplitude of the beat frequency carrier to be supplied tothe discriminator.

25. A television receiver for receiving a television signal bandincluding an amplitude modulated image carrier and a related frequencymodulated sound carrier spaced a substantially fixed frequency from thepicture carrier, said receiver comprising means to select and amplifyone such band of frequencies; means to heterodyne the carriers toproduce a new beat carrier having a frequency equal to the frequencyspacing of the two carriers; means for substantially preventing soundinterference with the video signal an output circuit for receiving thebeat frequency carrier and including a parallel resonant circuit inseries with a plate resistor; the parallel resonant circuit being tunedto the resultant heterodyned beat frequency; and a frequencydiscriminator tuned to said heterodyned frequency and energzed inaccordance with the voltage across said tuned circuit for deriving asound signal therefrom; and a reproducing device energized from thediscriminator.

26. A television receiver for receiving a television signal frequencyband including related video and audio signals on separate carriersseparated by a substantially fixed frequency difference, the videocarrier being amplitude modulated and the audio carrier being frequencymodulated, said re` ceiver comprising means for selecting the tele-.

vision band to bring in the two related carriers, means forsubstantially preventing sound interference with the video signal meansfor heterodyning the two carriers with each other to produce a'y beatfrequency carrier having a frequency ergized by the beat frequencycarrier to frequencydetect that carrier and obtain the audio signaltherefrom.

' LOUIS W. PARKER.

REFERENCES CITED The following references are of record in the 1 111e ofthis patent:

UNITED STATES PATENTS Number Name Date 1,495,470 Farrington May 27, 19241,681,564 Wright Aus. 21, 1928 1,735,134 Schroter Nov. 12, 1929 NumberName Dato Brand Mar. 24, 1931 Clements May 26, 1931 Adams June 23, 1931Braden Jan. 16, 1934 Holmes Oct. 6, 1936 Koch May 24, 1938 Kentner July4, 1939 Tubbs Mar. 11, 1941 Branson Sept. 30, 1941 Mailing Jan. 20, 1942-Hewe1 June 9, 1942 OTHER REFERENCES 15 Duplex 'Transmission of FM Soundand Facsimile, by Artzt, RCA Rev. 6:88-101, July 1941, Only page 96cited.

